Deep sequencing-based de novo transcriptome analysis reveals biosynthesis of gymnemic acid in Gymnema sylvestre (Retz.) Schult

Abstract

Abstract Gymnema sylvestre extract is used to cure the diabetes mellitus which is an important life style disease. Triterpene saponins having anti-diabetic property from G. sylvestre leaves belonging to oleanane and dammarene classes are collectively known as gymnemic acid. Genomic resources focused on biosynthesis of these molecules are not available. De novo transcriptome sequencing of leaf, flower and fruits of G. sylvestre genotype DGS-22 produced 60.95, 56.99 and 45.82 million raw reads. Quality raw reads were assembled into 112583, 203145 and 138343 set of unigenes for leaf, flower and fruit, respectively from which coding DNA sequences (CDSs) were predicted. Total of 71676, 99643 and 92770 CDSs were annotated against protein databases for leaf, flower and fruit, respectively. The Blast2GO was used to compare and determine the GO annotations. A total of 22933, 30420, 29631 and 33282 CDSs of leaf, flower, fruit and master assembly, respectively were assigned at least one GO term. Pathway mapping based on master assembly using KEGG database revealed probable candidate genes involved in gymnemic acid biosynthesis which showed that there were total of 287 CDSs encoding genes involved in the gymnemic acid pathway. Validation and expression profiling of nine genes through real time PCR showed up regulation of these genes in leaves of DGS 22 as compared to DGS 3 confirming efficient gymnemic acid biosynthesis in DGS 22 which was in accordance with chemo-profiling of these genotypes. Based on the available information from the master assembly, a putative pathway of the gymnemic acid biosynthesis is proposed.